Muffler having adjustable butterfly valve for improved sound attenuation and engine performance

ABSTRACT

A muffler to be coupled to the engine of a motor vehicle (e.g., a car, truck, motor cycle, boat, and the like) so that exhaust gases emitted by the engine can be exhausted to the atmosphere. The muffler includes an outer cylindrical body and an inner cylindrical liner having a plurality of apertures formed therethrough. Sound absorbing packing material is located in an annular space between the outer body and the inner liner. An adjustable butterfly valve is located within the inner liner and rotatable between open and closed positions to control the gas flow through the liner, the sound generated by the muffler as a result thereof, and the performance of the engine to which the muffler is coupled. The rotation of the butterfly valve is controlled by an external DC motor or a continuous cable. The shaft of the motor or the cable is connected through the outer body and inner liner of the muffler to the butterfly valve. By closing a manually accessible motor control switch electrically connected to the motor or by pulling on the cable, the operator of the motor vehicle has the ability to control the rotation of the butterfly valve connected to the motor shaft or the cable while the vehicle is in motion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved muffler for use with a motor vehicle, such as an automobile, truck, motorcycle, boat and the like. In particular, the improved muffler has an adjustable butterfly valve positioned therewithin so as to be rotatable between open and closed positions by the operator while the vehicle is in motion in order to selectively control the exhaust flow characteristics through the muffler, the corresponding sound generated by the muffler, and the performance of the engine to which the muffler is coupled.

2. Background Art

Virtually all engines that are manufactured today are coupled to a muffler so as to reduce the generation of sound as engine gases are exhausted to the atmosphere. For many motor vehicles, it is often possible to substitute a new muffler for the original stock muffler. Such a substitute muffler, which may be sold by the original manufacturer or as an after market product, is often purchased to alter the operating characteristics of the engine in a manner to suit the needs of the operator. For example, the substitute muffler may be selected to provide an improvement in engine performance. Particularly in the case of a car or a motorcycle, the substitute muffler may alter the range of sound produced by the engine exhaust. Motorcycle enthusiasts have long been aware of the impact to performance and sound (i.e., tone) that are offered by different mufflers having different sizes and shapes.

Most substitute mufflers are stagnant in that the operator is unable to change either the exhaust flow or sound characteristics once the muffler is installed on the motor vehicle. In this regard, it is known for such a substitute muffler to include a baffle located near the inlet end closest to the engine from which the gases are exhausted. However, locating a baffle adjacent the inlet end of the muffler has proved to be inefficient with respect to the ability to increase horsepower, to enable the engine to run cooler, and to improve fuel mileage.

What is even more, the conventional baffle is not adjustable while the motor vehicle is in motion. That is to say, after the original installation process has been completed, the operator has no means to dynamically adjust the orientation of the baffle across the muffler so as to affect the exhaust flow through the muffler and the corresponding sound generated by the muffler according to his wishes. Consequently, the operator is undesirably required to disassemble the muffler so as to gain access to and make internal changes to the orientation of the baffle. Then, the operator must reassemble the muffler for mounting back on the motor vehicle. Such a process of dismounting, disassembly and remounting can consume a large amount of time and result in errors by those who are not sufficiently skilled mechanics.

What is therefore desired is an improved muffler having a butterfly valve that can be selectively adjusted by the operator following installation of the muffler and while the motor vehicle is in motion so as to cause a corresponding adjustment in the flow of exhaust gases through the muffler and the sound produced by the muffler as a result thereof.

SUMMARY OF THE INVENTION

In general terms, disclosed below is a muffler to be ideally sold in the after market to replace a stock muffler manufactured for a motor vehicle (e.g., a car, truck, motorcycle, boat, and the like). The muffler includes a rotatable sound attenuating butterfly valve that is selectively adjusted while the motor vehicle is at idle or in motion in order to control the exhaust flow through the muffler, the corresponding sound generated by the muffler, and the performance of the engine to which the muffler is coupled.

The muffler includes a hollow, generally cylindrical outer body and a hollow, generally cylindrical inner liner that is spaced inwardly from the outer muffler body. A plurality of sound transmitting perforations are formed through the inner liner. Packed within an annular space between the outer muffler body and the inner liner are a pair of sound absorbing layers. A first sound absorbing layer lying adjacent the inner liner includes thin steel fibers that are woven together in the manner of steel wool. The second sound absorbing layer lying adjacent the outer muffler body is manufactured from fiberglass.

The sound attenuating butterfly valve is preferably a disc-shaped baffle which may include a number of holes formed therein. According to a first preferred embodiment, the butterfly valve is attached to one end of an elongated motor shaft which extends through the outer body and inner liner of the muffler, such that the butterfly valve is rotatable within and relative to the inner liner. In this case, the muffler is attached to an automobile. In a fully closed position, the butterfly valve extends across and blocks the inner liner, whereby the exhaust flow therethrough is diverted through the perforated inner liner and the sound level (in decibels) emitted by the muffler is minimized. In the fully open position, the butterfly valve is rotated 90 degrees so that the exhaust flow is unrestricted and the sound level emitted by the muffler is now maximized. To accomplish the foregoing, the butterfly valve is located at a particular position within the inner liner close to the outlet end of the muffler. While the precise location of the butterfly valve will depend upon the size and the shape of the muffler and the type of engine to which the muffler is coupled, it has been found that horsepower can be increased, the engine can be made to run cooler, and fuel economy improved when the butterfly valve is located within the inner liner a distance downstream from the inlet end of the muffler which lies in a range of distances between 60%-90% of the length of the outer muffler body.

A DC motor is mounted outside the muffler. A housing which encloses the motor is separated from the outer muffler body by a non-conductive spacer so as to reduce the transfer of heat from the muffler to the motor. The DC motor imparts a rotation to the motor shaft which causes a corresponding rotation of the butterfly valve between the closed and open positions within the inner liner. A suitable motor control (e.g., rocker) switch which is accessible in the passenger compartment of the automobile is manually closed by the operator to complete a circuit to the battery of the vehicle by which the motor is energized so as to rotate the motor shaft and the butterfly valve carried thereby. The switch is opened to break the circuit to the battery and thereby de-energize the motor at which time the motor shaft and the butterfly valve stop rotating to enable the muffler to produce an acoustic tone suitable to the operator.

According to a second preferred embodiment, the muffler is attached to a motorcycle. The butterfly valve in this case is connected to a pivot rod that extends through the outer muffler body, the perforated inner liner, and the pair of sound absorbing layers that are packed therebetween. A valve control cable is connected at one end thereof to a billet knob that is accessible to the operator of the motorcycle. The opposite end of the valve control cable is coupled to an integral adjustment arm that projects at an angle from the pivot rod at the exterior of the muffler. A pulling or pushing force applied to the cable by the operator is transmitted as a rotational force to the pivot rod via the adjustment arm. A rotation of the pivot rod is then imparted to the butterfly valve within the perforated inner liner to cause a corresponding rotation of the valve between the fully open and fully closed positions to selectively control the exhaust flow and the sound generated thereby.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a muffler for use on an automobile according to a preferred embodiment of this invention having a DC motor mounted outside the muffler body to cause a rotation of a sound attenuating butterfly valve;

FIG. 2 shows the butterfly valve carried by the shaft of the motor and rotatable therewith at the interior of the muffler of FIG. 1 to control the exhaust flow through and the sound generated by the muffler;

FIG. 3 is a partial cross-section showing the particular location of the rotatable butterfly valve within the muffler to achieve the engine performance benefits of this invention;

FIG. 4 shows the butterfly valve rotating 90 degrees within the muffler between fully closed and fully open positions;

FIG. 5 is an exploded view showing a motor housing to be mounted on a spacer outside the muffler body and the motor shaft extending from the motor housing to be attached to the butterfly valve for causing the butterfly valve to rotate; and

FIG. 6 is a cross-section of a muffler for use on a motorcycle and having a rotatable butterfly valve therewithin to control the exhaust flow through and the sound generated by the muffler.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring concurrently to FIGS. 1-4 of the drawings, there is shown a muffler 1 having particular application as an after market product for installation on a motor vehicle, such as an automobile. However, it is within the scope of the present invention for the muffler 1 to be installed on other motor vehicles, such as motorcycles, trucks, boats, and the like. The muffler 1 includes a hollow, generally cylindrical outer body 3 having a typical length of approximately fourteen to twenty four inches. The muffler 1 includes an inlet end 5 to receive exhaust gases from the engine of the automobile. Located opposite the inlet end 5 of muffler 1 is an outlet end 7 through which the exhaust gases are distributed to the atmosphere. Mounting brackets (not shown) may be located around the outer muffler body 3 so that the muffler 1 can be easily installed on the automobile as a retrofit substitute for a stock muffler.

In accordance with the present improvement, a rotatable sound attenuating butterfly valve 10 or similar baffle is positioned at a specific location inside the outer body 3 of muffler 1. As is best illustrated in FIG. 3, the butterfly valve 10 is shown positioned a distance (designated D) from the inlet end 5 of muffler 1. In this regard, it has been found that the overall performance of the engine with which muffler 1 is associated can be enhanced by locating the butterfly valve 10 closer to the outlet end 7 thereof rather than adjacent the inlet end 5 as has heretofore been common in conventional after market muffler configurations. More particularly, the distance D taken from the inlet end 5 of the muffler 1 to the location of the butterfly valve 10 should be at least 60 percent of the overall length of the outer muffler body 3. While the distance D will vary from one muffler to the next, depending upon the configuration of the muffler and the engine with which the muffler 1 is interfaced, it has been found that the best engine performance can be achieved by locating the butterfly valve 10 within the outer muffler body 3 at a particular distance D that lies within a range of distances from 60% to 90% downstream from the inlet end 5 of muffler 1.

The details of the muffler 1 are now disclosed while continuing to refer to FIGS. 1-4. The hollow outer muffler body 3 is preferably manufactured from stainless steel. Spaced radially inwardly from and coaxially aligned with the muffler body 3 between the inlet and outlet ends 5 and 7 of muffler 1 is a hollow, cylindrical inner liner 12 that is also preferably manufactured from stainless steel. The diameter of the hollow inner liner 12 must be sufficient to accommodate the rotatable butterfly valve 10 therewithin. As is best shown in FIGS. 3 and 4, the inner liner 12 has a plurality of exhaust transmitting perforations 14 formed therein. It has been found that the gas flow through perforations 14 as well as the horsepower of the automobile can be maximized when the perforations 14 in the inner liner 12 have a diameter of approximately 0.125 inches. A (e.g., stainless steel) collar 16 surrounds the inner liner 12 to provide structural reinforcement at a location along the liner 12 at which the butterfly valve 10 will be suspended for rotation in a manner that will be disclosed in greater detail hereinafter when referring to FIG. 5.

As is best shown in FIGS. 2-4, a pair of sound absorbing layers are packed in an annular space between the outer body 3 and the inner liner 12 of muffler 1. A first sound absorbing layer 18 lying adjacent the inner liner 12 is formed from steel fibers that are woven together in a manner similar to that known as steel wool. The second sound absorbing layer 20 lying adjacent the outer body 3 is formed from fiberglass. The sound absorbing layers (i.e., packings) 18 and 20 lie face-to-face one another within the outer body 3 of muffler 1 to absorb and reduce engine noise when exhaust gases are transmitted through the perforations 14 of the liner 12.

Details of the sound attenuating butterfly valve 10 and the means for controlling the rotation of butterfly valve 10 within the perforated inner liner 12 of muffler 1 are now described while referring to FIG.. 5 of the drawings. The butterfly valve 10 is preferably a disc-shaped plate or similar baffle having one or more exhaust transmitting holes 22 formed therein. The number and size of the holes 22 in butterfly valve 10 is dependent upon the type of engine with which the muffler 1 is associated. However, it is within the scope of this invention for the butterfly valve 10 to be totally devoid of holes or any other openings so as to have a solid, continuous face within the inner liner 12.

A 12 volt DC motor (not shown) is coupled to the butterfly valve 10 to control the orientation (i.e., rotation) thereof within the inner liner (designated 12 in FIGS. 2-4) that is surrounded by the outer muffler body 3. The motor is enclosed by a motor housing 24 having a mounting base 25 extending across the bottom thereof. In the assembled relationship of FIGS. 1-3, the motor housing 24 is seated atop and connected to a spacer 26 so as to be separated from the outer muffler body 3. In this regard, the spacer 26 is preferably manufactured from a solid block of non-heat conductive (e.g., resin, phenolic, or similar plastic) material so as to minimize the transfer of heat from the muffler 1 to the motor and thereby avoid a potential heat related motor malfunction. A series of vent holes 27 are formed in the spacer 26 through which to vent engine heat from the spacer 26 away from the motor. It has been found that a reduced volume, triangular-shaped spacer 26 maximizes the flow of air through the vent holes 27 for dissipating heat to the atmosphere.

The spacer 26 has a longitudinally extending channel 28 running therethrough to accommodate the motor shaft 30 which projects downwardly and outwardly from the motor housing 24, past the mounting base 25 and towards the muffler 1. A mounting pedestal 34 is affixed (e.g., welded) to the muffler body 3. In the assembled relationship, the spacer 26 is disposed between the mounting base 25 of motor housing 24 and the mounting pedestal 34 against muffler body 3. Each of the mounting base 25, the spacer 26 and the mounting pedestal 34 has a set of axially aligned holes 36, 37 and 38 to receive respective fasteners (e.g., socket head bolts) 40. The mounting pedestal 34 also has a channel 42 extending longitudinally therethrough and axially aligned with the channel 28 running through the spacer 26. The channel 42 through pedestal 34 continues through the outer body 3 and the perforated inner liner 12 of muffler 1 so that the butterfly valve 10 may be suspended and rotated within the inner liner 12 as shown in FIG. 3 and in a manner that will soon be described. To this end, the motor shaft 30 which projects outwardly from the motor housing 24 must have a sufficient length so as to be received inwardly of the outer muffler body 3 and through the perforated inner liner 12 via the channel 42 extending through the mounting pedestal 34.

With the fasteners 40 moved through the axially aligned holes 36-38, the motor housing 24 (at mounting base 25) and the spacer 26 are connected one above the other to the body 3 of muffler 1 at the mounting pedestal 34. The holes 38 in mounting pedestal 34 may be threaded to receive and releasably retain correspondingly threaded fasteners 40.

A lower end of the motor shaft 30 includes a recess 44. The recess 44 is sized to accommodate the butterfly valve 10 therewithin. In the embodiment illustrated in FIG. 5, the butterfly valve 10 is removably connected to the motor shaft 30 by means of fasteners 46 which are mated to shaft 30 by way of holes 48 formed in the valve 10 (best shown in FIG. 2). In this case, one butterfly valve 10 having some or no holes 22 can be replaced by a different butterfly valve having a different number of holes to match the characteristics of the particular engine with which the muffler 1 will be associated. However, it is to be understood that the butterfly valve 10 can also be permanently affixed to and carried by the motor shaft 30 such as by means of welding.

The motor within the motor housing 24 receives a DC current via a power cord 50. An electrical plug 52 is connected to one end of the power cord 50. The plug 52 is interconnected with the ignition system of the motor vehicle by mans of a suitable (e.g., 12 volt rocker) motor control switch or the like which is preferably mounted in the passenger compartment of the motor vehicle in easy reach of the operator. When the motor control switch is moved to a closed position while the motor vehicle is either in motion or at rest, an electrical circuit between the vehicle battery and the DC motor is completed, whereby the motor will be energized. Accordingly, the motor within motor housing 24 will now impart a rotational force to the motor shaft 30 so as to cause a rotation thereof relative to the perforated inner liner 12 that is surrounded by outer muffler body 3. A rotation of the motor shaft 30 causes a corresponding rotation of the butterfly valve 10 carried by shaft 30 within the inner liner 14 in the manner illustrated in FIG. 4. If the DC motor within motor housing 24 is reversible, the direction of rotation of the motor shaft 30 and the butterfly valve 10 carried thereby will depend upon the position of the manually operated (rocker) switch.

When the motor control switch is released or otherwise moved to an open or neutral switch position, the electrical circuit between the vehicle battery and the DC motor will be broken. Hence, current will now be removed from the motor, whereby the motor shaft 30 and the butterfly valve 10 that is carried thereby will no longer rotate. It may therefore be appreciated that the switch connected between the vehicle battery and the motor may be operated (i.e., closed) for a particular time in order to selectively orient (i.e., rotate) the butterfly valve 10 within the perforated inner liner 12 (of FIG. 4) to achieve the most advantageous sound attenuation characteristics and engine performance.

That is to say, by locating the butterfly valve 10 carried by the motor shaft 30 and rotatable within the perforated inner liner 12 which is surrounded by woven steel fiber and fiberglass layers 18 and 20, the sound attenuation characteristics of the muffler 1 can be enhanced. What is more, by positioning the butterfly valve 10 a distance (designated D in FIG. 2) between 60%-90% of the overall distance along the muffler body 3 downstream from the inlet end 5, the engine of the vehicle with which the muffler 1 is interfaced will experience greater horsepower and performance. In particular, the number of holes 22 (if any) through butterfly valve 10 and the position to which the butterfly valve 10 is rotated will enable the operator to control the exhaust flow from the vehicle engine and minimize the back pressure to which the engine is subjected. As indicated above, the type of engine will determine the precise placement of the butterfly valve 10 along the muffler body 3 and the number of holes 22 to be formed in the butterfly valve 10 that is carried by and rotated with the motor shaft 30.

It may be further appreciated that the butterfly valve 10 of muffler 1 is positioned at an entirely different location than that associated with most conventional after market mufflers. Instead of being positioned near the inlet end of the muffler, the butterfly valve 10 of the present invention is positioned significantly downstream (at least 60% from the inlet end) and closer to the outlet end. The precise distance D at which the butterfly valve 10 is positioned along the muffler body 3 is chosen to correspond with the characteristic “sweet spot” where the muffler 1 will be acoustically tuned and maximize horsepower.

When the butterfly valve 10 as shown and described herein is located at the sweet spot near the outlet end of the muffler 1, the engine horsepower has been found to exceed the horsepower that can be achieved when a butterfly valve or similar baffle is positioned at locations closer to the inlet end. For example, it has been found that as much as 25% more horsepower can be achieved when placing the butterfly valve 10 at position D near the outlet end 7 of muffler 1 as illustrated in FIG. 2 as opposed to a position adjacent the inlet end. In this same regard, it will be recognized that the muffler 1 with which the butterfly valve 10 is associated can be provided with a variety of sizes and shapes, depending upon the type of engine and the corresponding motor vehicle to which the muffler 1 is attached. The exact location of the sweet spot represented by the distance D will vary with the type of engine as well as the configuration of the muffler. A dynomonitor can be used to measure horsepower so that the ideal placement of the butterfly valve 10 can be determined in different mufflers. By way of example only, for a muffler having an outer muffler body 3 of fourteen inches, it has been found that the sweet spot and the corresponding position of butterfly valve 10 will fall a distance D of approximately nine inches downstream from the inlet end.

The ability to dynamically adjust the exhaust flow through the muffler 1 while the motor vehicle is in motion or at idle by virtue of the rotatable butterfly valve 10 will not only alter the level of sound emitted from the muffler 1 but will also reduce engine heat. That is to say, the exhaust flow through the muffler 1 and the level of sound (in decibels) generated by the muffler as a result thereof is controlled according to the position of the butterfly valve 10. The exhaust flow through muffler 1 will be restricted and the sound attenuated when the butterfly valve 10 is rotated to the fully closed position across the inner liner 12. In this case, most or all of the exhaust gases (depending upon the number of holes 22 in valve 10) will be directed outwardly of the perforations 14 in liner 12 and into the sound absorbing (i.e., packing) layers 18 and 20. On the other hand, the exhaust flow will be unrestricted and the sound emitted by the muffler will be maximized when the butterfly valve 10 is rotated 90 degrees from the fully closed position to the fully open position at which the inner liner 12 is no longer obstructed. By evacuating the engine exhaust more efficiently than that capable by a conventional muffler, the muffler 1 of the present invention may enable the engine to run cooler. Typically, a cooler operating temperature will result in improved fuel economy for the engine.

The muffler 1 shown in FIGS. 1-5 is particularly applicable for use on an automobile. FIG. 6 of the drawings shows a muffler 60 that is ideally suited for use on a motorcycle. Like the muffler 1, the muffler 60 includes a sound attenuating butterfly valve 62 that is located within an inner liner 64 having exhaust transmitting perforations 65 formed therewithin. A pair of sound absorbing layers 66 and 68 are packed face-to-face one another between the inner liner 64 and the outer body 70 of muffler 60. The sound absorbing layers 66 and 68 of muffler 60 may be identical to and perform the same function as the sound absorbing layers 18 and 20 of the muffler 1 of FIGS. 1-5.

The butterfly valve 62 is preferably a disc-shaped plate or similar baffle having one or more exhaust transmitting holes 72. Like the butterfly valve 10 described above, the butterfly valve 62 herein described is rotatable 90 degrees between fully open and fully closed positions across the perforated inner liner 64 by which to control the flow of exhaust gases from the engine of the motorcycle to the atmosphere and the corresponding sound produced thereby. Also like that earlier described, the positions of the butterfly valve 62 may be selectively and dynamically adjusted by the operator while the motorcycle is in operation or at idle to achieve sound attenuation characteristics and engine performance according to the wishes of the operator.

However, instead of coupling the butterfly valve to the shaft of a motor as described while referring to FIG. 5, the butterfly valve 62 shown in FIG. 6 is coupled to a valve control cable 74 that runs along the outer muffler body 70 so as to be manually accessible to the motorcycle operator. One end of the valve control cable 74 is connected to a billet knob 76 that may be grasped to enable the operator to apply a pulling or pushing force to the cable. The opposite end of the valve control cable 74 is coupled to a pivot rod 78. The pivot rod 78 extends through the inner liner and the outer body 64 and 70 of the muffler 60 and the sound absorbing layers 66 and 68 packed therebetween. One end of the pivot rod 78 is connected to the butterfly valve 62 at the interior of the perforated inner liner 64 such that a rotation of pivot rod 78 is imparted to butterfly valve 62 to cause a corresponding rotation thereof between the fully open and fully closed positions.

The opposite end of the pivot rod 78 includes an integral adjustment arm 80 that is coupled to the valve control cable 74 by means of a fastener 82. The adjustment arm 80 is bent so as to extend at an angle from pivot rod 78 to cable 74, whereby an axial (i.e., linear) pulling or pushing force applied to cable 74 by the motorcycle operator is transmitted as a rotational force to the pivot rod 78. In this same regard, a rotation of the pivot rod 78 is imparted to the butterfly valve 62 to cause a corresponding rotation thereof between the open and closed positions. The precise rotation of butterfly valve 62 is dependent upon the magnitude of the pushing or pulling force that is applied to the billet knob 76 of the valve control cable 74 by the motorcycle operator.

Dynomonitor tests were performed to document the improved performance of a muffler like that disclosed herein. Specifically, a muffler 60 for a motorcycle according to the teachings of this invention was compared, with the butterfly valve 62 rotated to fully open and fully closed positions across the perforated inner liner 64, to a Harley stock muffler, a Harley accessory muffler, and an aftermarket muffler known commercially as the Python II. The mufflers were installed on an 80 cubic inch evolution engine having a MSSR-I cam, an S&S carburetor, and Harley Ignition Model 32410-91. The test results are listed in the following table. While the test results were collected for the motorcycle muffler 60 of FIG. 6, and as has been explained above, the teachings of the present invention are suitable for use with other motor vehicles, such as an automobile, a truck or a boat.

2500 3000 4000 5000 6000 RPM H.P./D.B.A. H.P./D.B.A. H.P./D.B.A. H.P./D.B.A. H.P./D.B.A. Stock 18 80 26 81 41 82 41 83 42 85 Accessory 20 86 36 89 49 92 58 94 53 96 Python II 21 87 32 90 46 91 57 94 39 96 Valve Closed 20 80 29 81 44 83 52 84 51 85 Valve Open 23 82 35 83 50 85 61 88 69 89 H.P.: Horsepower D.B.A.: Decibels of sound 

1. A muffler to be coupled to the engine of a motor vehicle to receive gases therefrom to be exhausted to the atmosphere, said muffler comprising: a generally cylindrical outer body; a generally cylindrical inner liner spaced radially inward from said outer body and having a plurality of apertures formed therein, said inner liner receiving the gases from the engine to be exhausted to the atmosphere; an adjustable valve plate positioned within said inner liner and rotatable between open and closed positions; a rotatable shaft extending through said outer body and said inner liner and connected to said adjustable valve plate to impart a rotational force to said valve plate to cause said valve plate to rotate between said open and closed positions so as to control the gas flow through said inner liner; and means by which to enable the operator of said motor vehicle to control the rotation of said rotatable shaft and the corresponding rotational force imparted to said adjustable valve plate while the motor vehicle is in motion.
 2. The muffler recited in claim 1, wherein said means to enable the operator to control the rotation of said rotatable shaft to cause said valve plate to rotate between said open and closed positions with respect to said inner liner is a motor.
 3. The muffler recited in claim 2, wherein said motor is mounted on said muffler at a location outside the outer body of said muffler.
 4. The muffler recited in claim 3, further comprising a spacer interconnected between said motor and the outer body of said muffler, said spacer having a channel running longitudinally therethrough, and said rotatable shaft extending from said motor to the inner liner of said muffler via the channel of said spacer.
 5. The muffler recited in claim 4, wherein said spacer is manufactured from a non-heat conducting material so as to reduce the transfer of heat from the outer body of said muffler to said motor by way of said spacer.
 6. The muffler recited in claim 4, wherein said spacer has at least one vent opening formed therein through which heat transferred from the outer body of said muffler to said spacer is vented to the atmosphere and away from said motor.
 7. The muffler recited in claim 2, wherein said motor is a DC motor that is energized to cause said rotatable shaft and said valve plate connected thereto to rotate, said motor being energized by a DC current carried by an electrical power cord connected to said motor.
 8. The muffler recited in claim 7, further comprising a motor control switch connected to said electrical power cord, said motor control switch being accessible to and manipulated by the operator of the motor vehicle while the vehicle is in motion to control the energization of said DC motor and the corresponding rotation of said rotatable shaft and said valve plate connected thereto.
 9. The muffler recited in claim 1, wherein said valve plate is detachably connected to said rotatable shaft.
 10. The muffler recited in claim 1, wherein said valve plate has at least one gas transmitting hole formed therein.
 11. The muffler recited in claim 1, further comprising a layer of fiberglass located between the outer body and the inner liner of said muffler to absorb sound being transmitted thereto through the apertures formed in said inner liner.
 12. The muffler recited in claim 11, further comprising a layer of steel fibers located between the outer body and the inner liner of said muffler adjacent said fiberglass layer to absorb sound being transmitted to said layers of fiberglass and steel fibers through the apertures formed in said inner liner.
 13. The muffler recited in claim 1, wherein said valve plate is positioned within the inner liner of said muffler so as to lie at least 60% of the length of said inner liner downstream from the end of said inner liner at which the engine gases are received and closer to the opposite end of said inner liner at which the engine gases are exhausted to the atmosphere.
 14. A muffler to be coupled to the engine of a motor vehicle to receive gases therefrom to be exhausted to the atmosphere, said muffler comprising: an outer body; an inner liner spaced inwardly from said outer body and having a plurality of apertures formed therein, said inner liner receiving the gases from the engine to be exhausted to the atmosphere; an adjustable valve plate positioned within said inner liner and rotatable between open and closed positions; a motor; and a motor shaft extending from said motor and coupled to said valve plate through said outer body and said inner liner, said motor being energized to impart a rotational force to said motor shaft by which to cause said valve plate connected to said motor shaft to rotate between said open and closed positions to control the flow of engine gases through said inner liner.
 15. The muffler recited in claim 14, further comprising a motor control switch electrically connected to said motor, said motor control switch being accessible to and manipulated by the operator of the motor vehicle while the vehicle is in motion to control the energization of said motor and the corresponding rotation of said rotatable shaft and said valve plate coupled thereto.
 16. The muffler recited in claim 14, wherein said valve plate is positioned within the inner liner of said muffler so as to lie at least 60% of the length of said inner liner downstream from the end of said inner liner at which the engine gases are received and closer to the opposite end of said inner liner at which the engine gases are exhausted to the atmosphere.
 17. The muffler recited in claim 14, further comprising a sound absorbing packing material located between the outer body and the inner liner of said muffler to absorb sound transmitted thereto through the apertures formed in said inner liner.
 18. A muffler to be coupled to the engine of a motor vehicle to receive gases therefrom to be exhausted to the atmosphere, said muffler comprising: a generally cylindrical outer body; a generally cylindrical inner liner spaced radially inward from said outer body and having a plurality of apertures formed therein, said inner liner receiving the gases from the engine to be exhausted to the atmosphere; an adjustable valve plate positioned within said inner liner and rotatable between open and closed positions; a rotatable pivotable rod extending through said outer body and said inner liner and connected to said adjustable valve plate to impart a rotational force to said valve plate to cause said valve plate to rotate between said open and closed positions so as to control the gas flow through said inner liner; and a cable by which to enable the operator of said motor vehicle to control the rotation of said pivot rod and the corresponding rotational force imparted to said adjustable valve plate while the motor vehicle is in motion, an axial pulling or pushing force applied to said cable imparting a rotational force to said pivot rod for causing a rotation of said valve plate.
 19. The muffler recited in claim 18, wherein said pivot rod includes an arm that extends at an angle from said pivot rod to be coupled to said cable.
 20. The muffler recited in claim 18, further comprising a sound absorbing packing material located between the outer body and the inner liner of said muffler to absorb sound transmitted thereto through the apertures formed in said inner liner. 